The objective of this project is to test the tumorigenic effect of long-term elevation of serum gonadotropins on the interstitial cells of the testis and the consequent carcinogenic effect of elevated endogenous testosterone levels on prostatic epithelium. This is attained in young rats by parabiosing an oophorectomized female to an intact male. The effect is augmented by removing a kidney from each member of the pair. A further objective is to determine whether the antihormone drugs Danazol, Cyproterone and Nafoxidine are effective in preventing the development of tumors of the testis and prostate induced by the hormonal stimulation.